1. Field of the Invention
The invention relates to a control apparatus and a control method for an internal combustion engine, and in particular, relates to an ignition timing control executed when the internal combustion engine is operated at low speed.
2. Description of the Related Art
Ignition timing control in which ignition timing is accurately controlled in accordance with operating conditions of an engine is commonly practiced as a part of engine control. As one mode of such ignition timing control, control for efficiently operating an engine is executed, in which a fixed ignition process is performed during a start-up of the engine so as to maintain the ignition timing at a predetermined angle in order to improve startability of the engine, and after the start-up of the engine, a shift is made from the fixed ignition process to a calculation ignition process in which the optimal ignition timing calculated based on the operating conditions of the engine is set.
For example, Japanese Patent Application Publication No. 5-256237 (JP-A-5-256237) describes a configuration of an ignition angle control apparatus by which it is possible to suppress occurrence of knocking even when the engine is restarted at high temperature. In the configuration, the ignition angle is determined based on a crank angle signal (rotary phase signal) that is retarded in terms of time by retarding means. In this configuration, even at the time of engine start when it is difficult to determine the optimal ignition angle based on an engine speed and other operating state quantities, it is possible to substantially retard the ignition angle, whereby occurrence of knocking is suppressed even at the time of engine restart at high temperature.
Further, Japanese Patent Application Publication No. 2006-002618 (JP-A-2006-002618), Japanese Patent Application Publication No. 2005-214125 (JP-A-2005-214125), and Japanese Patent Application Publication No. 6-017730 (JP-A-6-017730) describe related arts pertaining to the ignition timing control executed at the time of engine start.
On the other hand, the engine speed during idling operation of the engine (hereinafter referred to as “idling speed”) is set low in order to improve fuel consumption. In this specification, “engine speed” indicates a number of rotation per unit time (e.g. a number of rotation per minute: rpm).
When the idling speed is set low in this way, in the ignition timing control in which the fixed ignition process is performed when it is detected that the engine is during a start-up based on the engine speed, there is a possibility that the engine may stall due to decreased output if the ignition timing is simply retarded at high temperature for the purpose only of suppressing occurrence of knocking, as described in JP-A-5-256237. However, the descriptions of the ignition timing control in JP-A-5-256237, JP-A-2006-002618, JP-A-2005-214125, and JP-A-6-017730 do not mention the possibility of engine stall caused by retardation of the ignition timing.